Download or read book Photofragment Ion Imaging in Photodissociation Dynamics written by Bogdan Radu Cosofret and published by . This book was released on 2003 with total page 334 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Photodissociation Dynamics of Nitrosyl Chloride written by Jadwiga Anna Milkiewicz and published by . This book was released on 2013 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Application of Ion Imaging and Laser induced Gratings to Chemical Dynamics written by Mark Anthony Buntine and published by . This book was released on 1992 with total page 468 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Photodissociation Dynamics of CH2I2 OCS and CH3CHO written by Benjamin W. Toulson and published by . This book was released on 2016 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1 outlines the focus of this thesis, understanding the mechanism of breaking a chemical bond following absorption of light.In Chapter 2 the design, construction and calibration of a new velocity-map direct current slice ion imaging (VMI) time-of-flight mass spectrometer is described. Wavelength tunable pulsed lasers are used to selectively pump (dissociate) a target molecule and probe (ionize) the fragments. Combing the techniques allows correlated photofragment quantum state distributions to be explored.Chapter 3 investigates the near-UV photodissociation dynamics of CH 2I2 using ion imaging over a range of excitation wavelengths. Ground state I(2P3/2) and spin-orbit excited I*( 2P1/2) atoms were probed using 2+1 resonance-enhanced multiphoton ionization (REMPI) or with single-photon VUV ionization. Analysis of the ion images shows that, regardless of iodine spin-orbit state, ~20% of the available energy is partitioned into translation ET indicating that the CH2I co-fragment is formed highly internally excited. A refined C--I bond dissociation energy of D0 = 2.155+/-0.008 eV is determined.In Chapter 4 the photoproducts of OCS after UV excitation have been followed with photofragment excitation spectroscopy (PHOFEX), using REMPI to state-selectively monitor S(1D) and S(3P2,1,0) products while the pump wavelength was scanned. Probing the major S(1D) product results in a broad, unstructured action spectrum that reproduces the overall shape of the first absorption band. In contrast spectra obtained probing S(3P) products display prominent resonances superimposed on a broad continuum; the resonances correspond to the diffuse vibrational structure observed in the conventional absorption spectrum. The vibrational structure is assigned to four progressions, each dominated by the C--S stretch, following direct excitation to quasi-bound singlet and triplet states. The results confirm a recent theoretical prediction that direct excitation to the 23A" state can occur in OCS.In Chapter 5 ion imaging measurements of CH3 fragments from photolysis of CH3CHO reveal multiple pathways to the same set of products. By systematically exploring product formation over a timescale of picoseconds to nanoseconds, and wavelengths between 265-328 nm, an evolving picture of the dynamics is found. Evidence to suggest that the three-body CH3+CO+H pathway remains closed at all wavelengths is presented.
Download or read book Photodissociation Dynamics of Small Organic Compounds Studied Using Photofragment Velocity Map Imaging written by Yi Liu and published by . This book was released on 2006 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Imaging in Molecular Dynamics written by Benjamin J. Whitaker and published by Cambridge University Press. This book was released on 2003-06-05 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt: Charged particle imaging has revolutionized experimental studies of photodissociation and bimolecular collisions over the past couple of decades. Written in a tutorial style by some of the key practitioners in the field, this book gives a comprehensive account of the technique and describes many of its applications.
Download or read book Imaging in Chemical Dynamics written by Arthur G. Suits and published by . This book was released on 2001 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive review of the rapidly growing field of imaging-based probes of chemical dynamics. It includes discussions of state-resolved photodissociation dynamics, orbital alignment and vector correlations, radical photodissociation, surface scattering, imaging photoelectron spectroscopy, ultrafast dynamics and coincidence techniques.
Download or read book Photodissociation Studies Using Velocity Ion Imaging Method High level Ab Initio Calculations of Molecular Energetic and Spectroscopic Properties and Benchmarking with Experiments written by Kai-Chung Lau and published by . This book was released on 2004 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Imaging Nuclear Motion During the Photofragmentation of Halomethane Molecules Triggered by Ultraviolet Light written by Farzaneh Ziaee and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the photoexcitation of molecules and visualizing the ensuing dynamics on their natural time scale is essential for our ability to describe and exploit many fundamental processes in different areas of science and technology. Prominent examples of such processes include, among many others, the adverse impacts of different classes of molecules on the ozone layer in atmospheric chemistry, light conversion into electricity through photovoltaics, photocatalysis, and some essential biological processes like vision and photosynthesis. Studies of molecular dynamics triggered by photon-molecule interaction underpin our understanding of many of these phenomena by adding the intermediate state to the "before-and-after" view of such photochemical or photobiological reactions. While identifying the initial molecular structure at equilibrium and determining the final products are crucial steps for the reaction characterization, understanding the dynamics connecting these initial and final states is essential for comprehending how the reaction really happens and potentially controlling its outcome. In other words, besides the "static" view of photo-induced reactions, identifying all intermediate states involved and mapping their spatio-temporal evolution are of great interest and importance. Since photoexcitation often induces coupled electron and nuclear motion on Angström spatial and femtosecond time scales, resolving such dynamics in space and time represents a significant scientific and technological challenge. Experimental tools to address this challenge have recently become available with the development of femtosecond lasers and imaging techniques capable of visualizing the evolving molecular structure. The present thesis aims to investigate the photodissociation dynamics of halomethane molecules triggered by ultraviolet (UV) light using coincidence ion momentum imaging as a primary structural characterization tool. Halomethanes are often considered as prototypical systems for molecular photodissociation in the UV domain. Due to the complicated excited-state structure driving the photochemistry of these molecules, they exhibit rich dynamics while being small enough to still allow for a detailed theoretical treatment. The primary goal of this work is to disentangle the photo-induced reaction channels, including direct and indirect dissociation pathways, and to visualize the motion of the individual molecular fragments in each of these channels. The photofragmentation reactions considered here include two- and three-body dissociation, transient isomerization and molecular halogen formation. The experiments are carried out at two different excitation wavelengths, 263 nm and 198 nm, which enables varying the dominant reaction pathways. To carry out these measurements, the 3rd and 4th harmonics of a 790 nm Ti: Sa femtosecond laser are used to initiate the dynamics of interest, which are then probed by multiple ionization and Coulomb explosion induced by an intense 790 nm pulse arriving after a variable time delay. The ions created in such pump-probe experiments are detected employing COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS). To facilitate interpreting the experimental results, they are compared to an extensive set of Coulomb explosion simulations. More specifically, this thesis describes three major studies. The first one is a set of time-resolved measurements on iodomethane (CH3I) photodissociation in the A-band, one of the best-studied reactions in ultrafast photochemistry. Here, the focus is on a detailed characterization of direct dissociation dynamics by Coulomb explosion imaging (CEI) and disentangling the competing reaction pathways involving single- and multi-photon excitations. The coincident measurement mode and an improved time resolution of 40-45 fs allowed us to observe a new feature in the two-body CEI pattern of this well-studied reaction, which was predicted theoretically but not yet observed experimentally, and to identify signatures of two- and three-photon processes populating Rydberg and ionic states. The second part of this work focuses on time-resolved studies of bromoiodomethane (CH2BrI) and chloroiodomethane (CH2ICl) photofragmentation in the A-band at 263 nm and, in particular, on imaging the co-fragment rotation. Here, the main objectives are to evaluate the effects of halogen-atom substitution on molecular dynamics and map the time evolution of individual photodissociation pathways. For these molecules, photoabsorption in the A-band predominantly breaks the C-I bond, with weaker but non-negligible contribution from the C-Br (or C-Cl) bond cleavage. Coincident two-body CEI analysis is used to map both of these channels, as well as a minor contribution from molecular halogen (IBr or ICl) formation. Three-body CEI patterns offer a deeper insight into the dynamics of these reactions and, in addition, reveal clear signatures of the three-body dissociation, which - at this wavelength - is most likely driven by the two-photon absorption. The three-body analysis also suggests that some fragmentation pathways pass through a transient linearized configuration, which is reached within ~100 fs from the initial photoabsorption and decays on a comparably fast time scale. One of the interesting aspects of dihalomethanes photodissociation in the A-band is that, unlike CH3I, where the excess energy is primarily channeled into translational motion, a significant portion of the available energy is partitioned into rotational excitation. Carbon-halogen bond cleavage results in the rotation of the molecular co-fragment, which can be unambiguously traced in the coincident three-body CEI maps for the corresponding dissociation channel. In this work, such rotational motion is directly imaged for the dissociation of either halogen atom, resulting in a "molecular movie" of the dissociating and rotating molecule. The third group of experiments described in this thesis includes time-resolved studies of bromoiodomethane and diiodomethane (CH2I2) photofragmentation in the B-band at 198 nm. In this part, the main goal is to trace the wavelength dependence of the photochemical reaction pathways. For CH2BrI, we observe a reversal of the branching ratio of C-I and C-Br bond cleavage compared to the 263 nm data, in agreement with earlier spectroscopic and theoretical studies. However, at 198 nm, three-body dissociation and molecular halogen formation become dominant photofragmentation channels for both molecules. Finally, the CH3I photodissociation is also studied in the B-band at 198 nm, where the excitation of the lowest-lying Rydberg states is expected to trigger pre-dissociation dynamics. Although no in-depth data analysis and modeling for this reaction have been carried out, the two-body CEI results clearly demonstrate the pre-dissociation nature of CH3I fragmentation at this wavelength, reflected in a broad, diffuse dissociation band, which is very different from distinct dissociation features observed for direct dissociation processes. Moreover, the data exhibit a pronounced oscillatory structure with a periodicity of 130-140 fs, which is visible only within the pre-dissociation lifetime of the excited state (~1.5 ps). While the exact origin of this structure remains unclear and will be a subject of further analysis and theoretical work, it most likely reflects the bound-state vibrational motion, which lasts until it pre-dissociates. The work presented in this thesis represents a significant step towards a better understanding of the UV-driven photochemistry of halomethanes and contains several examples of direct visualization of the atomic motion during these photochemical reactions. Our experimental approach enabled us to identify and disentangle different dissociation pathways and track their time evolution. The experimental methodology described here can be directly applied to investigate the light-driven nuclear motion in other molecular systems with different light sources.
Download or read book Studies of Photoinduced Molecular Dynamics Using a Fast Imaging Sensor written by Craig S. Slater and published by Springer. This book was released on 2015-10-15 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work presented in this thesis involves a number of sophisticated experiments highlighting novel applications of the Pixel Imaging Mass Spectrometry (PImMS) camera in the field of photoinduced molecular dynamics. This approach represents the union of a new enabling technology (a multiple memory register, CMOS-based pixel detector) with several modern chemical physics approaches and represents a significant leap forward in capabilities. Applications demonstrated include three-dimensional imaging of photofragment Newton spheres, simultaneous electron-ion detection using a single sensor, and ion-ion velocity correlation measurements that open the door to novel covariance imaging experiments. When combined with Coulomb explosion imaging, such an approach is demonstrated to allow the measurement of molecular structure and motion on a femtosecond timescale. This is illustrated through the controlled photoexcitation of torsional motion in biphenyl molecules and the subsequent real-time measurement of the torsional angle.
Download or read book Photodissociation Dynamics Studies Via Photofragment Translational Spectroscopy written by Niels E. Sveum and published by . This book was released on 2006 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Photofragment Ion Imaging written by Leon John Rogers and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Photoisomerization and Photodissociation Dynamics of Reactive Free Radicals written by Ryan Tyler Bise and published by . This book was released on 2000 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Photodissociation Dynamics of Halogen Oxide Species written by Kristin S. Dooley and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this dissertation is the study of the photodissociation dynamics of halogen oxide species (XO, X = Cl, Br, I). These radical species are known to be important in stratospheric and tropospheric ozone depletion cycles. They are also useful benchmark systems for the comparison to current theoretical methods where they provide insight into the dynamics occurring beyond the Franck-Condon region. These systems are studied using velocity map ion imaging, a technique that measures velocity and angular information simultaneously. Photofragment species are state-selectively ionized for detection using 2+1 REMPI (Resonance Enhanced Multi-Photon Ionization). The instrumentation employs a molecular beam of the XO radicals formed using pyrolitic and photolytic methods. The current work involves the measurement of fundamental physical constants of the XO species. The bond dissociation energy of IO is measured. Vibrational level dependent correlated final state branching ratios of the predissociation of the A(^2 II_3/2) state of ClO and BrO are reported, and comparison to theoretical methods is discussed.
Download or read book Research in Chemical Kinetics written by Bozzano G Luisa and published by Elsevier. This book was released on 2012-12-02 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research in Chemical Kinetics, Volume 1 focuses on authoritative review articles on a wide range of developing topics in the kinetics of gaseous and condensed phases. The selection first elaborates on gas-phase kinetics of free radicals studied by pulse radiolysis combined with time-resolved infrared diode laser spectroscopy and solid/liquid reactions of environmental significance. Discussions focus on coprecipitation of phosphate with calcite, reactions of silica and quartz, infrared spectroscopy of free radicals, and kinetics of methyl radicals. The book then examines the collision energy dependence of reaction cross sections and photoelectrochemical dynamics, including organometallic photoelectrochemistry and photofragmentation voltammetry, contrasting reactivity of ion radical excited states, photoelectrochemical reaction mechanisms, and experimental methods. The publication tackles collisional electronic energy transfer in CN free radicals, photo-ion imaging techniques and future directions in reactive scattering, and photoelectrochemical dynamics. Topics include photoelectrochemical reaction mechanisms, photoelectrochemical measurement of quantum yields, photofragment translational spectroscopy, and velocity distributions. The selection is a valuable reference for researchers interested in the kinetics of gaseous and condensed phases.
Download or read book Coincidence and Noncoincidence Studies of the Photodissociation Dynamics of Free Radicals written by Ann Elise Faulhaber and published by . This book was released on 2005 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book State selected Study of Ion molecule Reaction Dynamics Photodissociation Dynamics and Free Radical Studies Using Synchrotron Radiation written by Tao Zhang and published by . This book was released on 2003 with total page 406 pages. Available in PDF, EPUB and Kindle. Book excerpt:
